This invention relates generally to grid and spring subassemblies for bedding and furniture foundations for mattresses and seat cushions. Foundations for mattresses, typically referred to as box spring assemblies, conventionally consist of a support frame, a wire grid positioned above the support frame, and springs supporting the grid on the frame for yieldable movement under load toward the frame.
The metal components of a box spring assembly include the springs and the grid and in some cases the support frame. In this invention, the springs and grid are assembled into a subassembly which is supplied to the bedding or furniture manufacturer for final assembly and ultimate sale. In the case of box spring assemblies, various sizes and grades are made by the manufacturer and this requires the maintenance by the furniture manufacturer of a large inventory of metal component subassemblies. It is necessary that the spring subassemblies be assembled in such a manner that the springs will not become detached from the grid or move out of the proper position on the grid during transport and handling. One way of assuring that the springs stay attached to the grid is to use clips to attach the springs to the grid. However, the use of clips, of which several are needed for a box spring assembly, dramatically increases the number of components needed in the metal subassembly. In addition, certain types of loading applied directly to a cross wire can cause the clips to open and the springs to loosen from the grid.
Box spring assemblies have been developed in which the springs and the wire grid are interfit with one another in an "over and under" relationship with the grid to attach the spring to the grid. However, until the lower ends of the springs are attached to the support frame, it is possible to move the springs out of the desired position on the grid by inadvertent contact with the springs. It is also possible to inadvertently remove the springs from the grid. Such detachment or movement creates difficulties when the spring and grid subassembly is attached to the support frame due to misposition or loss of the springs. Examples of interfitting spring and grid subassemblies are shown in U.S. Pat. Nos. 4,339,834; 4,921,228 and 4,932,535.
It is an object of the present invention to provide a grid and spring subassembly in which the springs are secured to the grid without spring clips but in a manner which assures retention of the springs on the grid at all times.
Because spring and grid subassemblies must be transported from the subassembler to the final furniture assembler, it is beneficial if the subassemblies are stackable. Examples of stackable subassemblies are shown in co-pending patent applications Ser. No. 07/628,086 filed Dec. 17, 1990 entitled NESTABLE SPRING ASSEMBLIES FOR BEDDING AND FURNITURE and Ser. No. 07/656,585 filed Feb. 19, 1991 entitled STACKABLE SPRING ASSEMBLIES WITH FORMED WIRE SPRING MODULES. Both of these applications are commonly assigned with the present application and are hereby incorporated by reference.
According to the present invention, the grid cross wires are formed with periodic vertical offsets. The upper ends of the springs include attaching portions that are configured with at least one pair of segments in each spring transverse to the cross wire. These transverse segments are connected by a return bent portion so as to enable the spring attaching portion to be interfit with the cross wire at the vertical offset with one transverse segment overlying the vertically offset of the cross wire and the other transverse segment underlying the cross wire adjacent the vertical offset.
The cross wire is seated in the return bent portion between the two transverse segments. This interfitting engagement is accomplished by moving the spring attaching portion horizontally into engagement with the cross wire. In the engaged position, a longitudinal segment of the spring attaching portion extends parallel to the vertical offset of the cross wire but is vertically above the offset and horizontally to one side of the offset, opposite from the return bent portion.
After engagement, the vertical offset is plastically deformed vertically to a position along side a longitudinal segment of the spring attaching portion to entrap the longitudinal segment on the opposite side of the cross wire from the return bent portion of the spring attaching portion. This prevents withdrawal of the spring attaching portion from engagement with the cross wire in a direction normal to the cross wire while the over-under engagement relationship of the spring attaching portion to the cross wire prohibits movement in all other directions.
The plastic deformation of the cross wire offset results in a permanent attachment of the spring to the cross wire. The spring can only be detached from the cross wire by permanent deformation of the cross wire.
Preferably, the springs are configured in a V-shape to enable a plurality of grid and spring subassemblies to be stacked one upon the other with the lower portion of the spring being inserted into the rectangular pockets formed between cross wires in the grid stacked below.
Further objects, features and advantages of the invention will become apparent from a consideration of the following description and the appended claims when taken in connection with the accompanying drawings.